Semiconductor device and method of manufacturing the same, circuit board, and electronic instrument

ABSTRACT

A semiconductor device comprising: a semiconductor element having a plurality of electrodes; a passivation film formed on the semiconductor element in a region avoiding at least a part of each of the electrodes; a conductive foil provided at a given spacing from the surface on which the passivation film is formed; an external electrodes formed on the conductive foil; intermediate layer formed between the passivation film and the conductive foil to support the conductive foil; and wires electrically connecting the electrodes to the conductive foil; wherein a depression tapered in a direction from the conductive foil to the passivation film if formed under a part of the conductive foil that includes the connection with the external electrodes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and method ofmanufacture thereof, a circuit board and an electronic instrument.

2. Description of Related Art

As higher mounting density of semiconductor devices is demanded,bare-chip mounting is ideal. However, for bare chips, quality assuranceand handling are difficult. In response to this, semiconductor deviceshave been developed to which Chip Scale/size Package (CSP) technology isapplied. There is no formal definition of CSP, but generally this refersto an IC package in which the package size is the same as or only veryslightly larger than the chip size. The development of CSP technology isvery important as high-density mounting advances. One prior artpublication relating to CSP is International Patent PublicationWO95/08856.

According to this, a gap is formed between a substrate having externalelectrodes and a semiconductor chip, and into this gap resin isinjected. This resin is such as to have resilience once cured. By meansof this resilient resin, stress (thermal stress) applied to the externalelectrodes is absorbed. It should be noted that this stress is caused bythe difference in coefficient of thermal expansion between thesemiconductor device and the circuit board on which the semiconductordevice is mounted.

However, the resin injected between the semiconductor chip and thesubstrate is extremely thin, and for this reason it has not beenpossible adequately to absorb the thermal stress.

SUMMARY OF THE INVENTION

The present invention solves this problem, and has as its object theprovision of a semiconductor device and method of manufacture thereof, acircuit board and an electronic instrument such that thermal stress canbe effectively absorbed.

(1) According to a first aspect of the present invention, there isprovided a semiconductor device comprising:

a semiconductor element having a plurality of electrodes;

a passivation film formed on the semiconductor element in a regionavoiding at least a part of each of the electrodes;

a conductive foil provided at a given spacing from the surface on whichthe passivation film is formed;

external electrodes formed on the conductive foil;

an intermediate layer formed between the passivation film and theconductive foil to support the conductive foil; and

wires electrically connecting the electrodes to the conductive foil;

wherein a depression opening between the conductive foil and thepassivation film, is formed in the intermediate layer under a part ofthe conductive foil that includes the connection with the externalelectrodes.

The term “semiconductor element” relating to the present invention isnot restricted to a semiconductor chip, but may also include referenceto a wafer form not yet separated into chips. In other words, here a“semiconductor element” may be in any form so long as it is a portion ofa base substrate formed of for example silicon on which a circuit isformed, and which can be used once in the separated state, or equally tothe same while in the integral state.

According to this aspect of the present invention, the externalelectrodes are formed on the conductive foil, and the conductive foil issupported by the intermediate layer. A depression is formed in theintermediate layer, and the external electrodes are positioned over thedepression. In other words, the external electrodes are not supporteddirectly by the intermediate layer, but rather is floating on theintermediate layer. By this means, since the external electrodes areable to move relatively freely, the stress (thermal stress) generated bythe difference in coefficient of thermal expansion with the circuitboard can be absorbed.

(2) The depression may be filled with a resin having a Young's moduluslower than that of the intermediate layer.

In this way, since the space in the depression can be filled, thegeneration of cracks caused by the expansion of steam when heat isapplied, for example during reflow processes, can be prevented.

(3) The wires may be formed on the surface on which the passivation filmis formed, and may be positioned on the bottom surface of theintermediate layer depression; and the resin may have a conductingfiller added, and may electrically connect the wires to the conductivefoil.

(4) The intermediate layer may have a bevel between the electrodes andthe conductive foil; and the wires may be formed on the bevel toelectrically connect the electrodes to the conductive foil.

(5) The intermediate layer may be formed of a flexible material.

In this way, the intermediate layer itself can also relieve stress.

(6) The conductive foil may have a hole positioned within an openingedge of the depression and avoiding the connection with the externalelectrodes.

In this way, the conductive foil is more easily deformed, and stress canbe absorbed by the conductive foil.

(7) The semiconductor device may further comprise a substrate with asurface on which the conductive foil is formed facing toward theintermediate layer; the substrate may have a penetrating hole over thedepression; and the external electrodes may be formed on the conductivefoil through the penetrating hole.

By means of this, the conductive foil is covered by the substrate andthus protected.

(8) A substrate formed of a flexible material may be provided betweenthe intermediate layer and the conductive foil; the substrate may have apenetrating hole in a region avoiding above the depression; and thewires and the conductive foil may be electrically connected through thepenetrating hole.

(9) The conductive foil and the wires may be formed integrally.

(10) The conductive foil and the wires may be formed separately.

(11) According to a second aspect of the present invention, there isprovided a method of manufacturing a semiconductor device, comprisingthe steps of:

providing a semiconductor element that includes a plurality ofelectrodes and a passivation film that is formed on a surface of thesemiconductor element in a region avoiding at least a part of each ofthe electrodes;

forming a conductive foil at a given spacing from the surface on whichthe passivation film is formed, an intermediate layer between thepassivation film and the conductive foil to support the conductive foil,and a depression in the intermediate layer in a position to avoid theelectrodes;

forming wires that connect electrically the electrodes to the conductivefoil; and

forming external electrodes on the conductive foil in a position abovethe depression.

With a semiconductor device manufactured according to this aspect of thepresent invention, the external electrodes are formed on the conductivefoil, and the conductive foil is supported by the intermediate layer. Adepression is formed in the intermediate layer, and the externalelectrodes are positioned over the depression. In other words, theexternal electrodes are not supported directly by the intermediatelayer, but rather are floating on the intermediate layer. By this means,since the external electrodes are able to move relatively freely, thestress (thermal stress) generated by the difference in coefficient ofthermal expansion with the circuit board can be absorbed.

(12) In the method of the present invention, a substrate may beprovided, having a penetrating hole, and having the conductive foiladhered to a position including the position over the penetrating hole;the intermediate layer may be formed on the surface on which thepassivation film is formed, and the depression may be formed in theintermediate layer; thereafter, the substrate may be mounted on theintermediate layer so that the penetrating hole is positioned over thedepression and that the conductive foil is opposed to the depression;and the external electrodes may be formed on the conductive foil throughthe penetrating hole.

By means of this, since the conductive foil is adhered to the substrate,the step of forming the conductive foil can be carried out simply.

(13) In the method of the present invention, a substrate formed of aflexible material and having a penetrating hole may be provided; theintermediate layer may be formed on the surface on which the passivationfilm is formed, the depression may be formed on the intermediate layer,and the wires may be formed on the intermediate layer; and the substratemay be mounted on the intermediate is layer with the penetrating holepositioned over the wires, the conductive foil may be formed on thesubstrate, and the wires and the conductive foil may be electricallyconnected through the penetrating hole.

By means of this, since the conductive foil is adhered to the substrate,the step of forming the conductive foil can be carried out simply.

(14) The intermediate layer may be formed on the surface on which thepassivation film is formed, the conductive foil may be formed on theintermediate layer, a hole may be formed in the conductive foil, and theintermediate layer may be etched through the hole to form thedepression.

(15) The intermediate layer may be formed of a material which can beetched under conditions in which the semiconductor element cannot beetched.

In this way, when the intermediate layer is etched, etching of thesurface of the semiconductor element can be prevented.

(16) The passivation film may be etched under the etching conditions ofthe intermediate layer; and

on the passivation film, a covering layer may be formed of a materialwhich is not readily etched under the etching conditions of theintermediate layer, the intermediate layer may be formed on the coveringlayer, the conductive foil may be formed on the intermediate layer, ahole may be formed in the conductive foil, and the intermediate layermay be etched through the hole to form the depression.

In this way, by the formation of the covering layer on the passivationfilm, the passivation film is prevented from being etched.

(17) The passivation film may be etched under the etching conditions ofthe intermediate layer;

on the passivation film, a first covering layer may be formed of amaterial which is not readily etched under the etching conditions of theintermediate layer;

the intermediate layer may be formed on the first covering layer;

the conductive foil and wires may be formed on the intermediate layer,and a hole may be formed in the conductive foil;

a solder resist layer may be formed on the wires;

on the solder resist layer, a second covering layer may be formed of amaterial which is not readily etched under the etching conditions of theintermediate layer; and

the intermediate layer may be etched as far as the underneath of theconductive foil through the hole in the conductive foil.

(18) The method of the present invention may further comprise, beforethe step of etching the intermediate layer, a step in which the externalelectrodes are formed on the conductive foil, and on the externalelectrodes an electrode covering layer is formed of a material which isnot readily etched under the etching conditions of the intermediatelayer.

By means of this, after the external electrodes are formed, thedepression is formed by etching the intermediate layer. Therefore, sincethe residue created by the formation of the external electrodes areremoved before carrying out etching, no residue remains in thedepression.

(19) The method of the present invention may further comprise a step inwhich the depression is filled with a resin having a Young's moduluslower than that of the intermediate layer.

(20) According to a third aspect of the present invention, there isprovided a circuit board on which is mounted the semiconductor devicedescribed above.

(21) According to a fourth aspect of the present invention, there isprovided an electronic instrument having the circuit board describedabove.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a first embodiment of thesemiconductor device.

FIG. 2 is a plan view showing the first embodiment of the semiconductordevice.

FIGS. 3A to 3E show the method of manufacturing the first embodiment ofthe semiconductor device.

FIG. 4 shows a second embodiment of the semiconductor device.

FIG. 5 shows a third embodiment of the semiconductor device.

FIG. 6 shows a fourth embodiment of the semiconductor device.

FIGS. 7A to 7D illustrate the method of manufacturing the fourthembodiment of the semiconductor device.

FIGS. 8A to 8C illustrate the method of manufacturing the fourthembodiment of the semiconductor device.

FIGS. 9A to 9C show the method of manufacturing a fifth embodiment ofthe semiconductor device.

FIGS. 10A to 10C show the method of manufacturing a sixth embodiment ofthe semiconductor device.

FIGS. 11A and 11B show a seventh embodiment of the semiconductor device.

FIG. 12 shows an eighth embodiment of the semiconductor device.

FIGS. 13A to 13D show the method of manufacturing a ninth embodiment ofthe semiconductor device.

FIGS. 14A and 14B show the method of manufacturing the ninth embodimentof the semiconductor device.

FIG. 15 shows a modification of the ninth embodiment.

FIG. 16 shows a circuit board on which is mounted this embodiment of thesemiconductor device.

FIG. 17 shows an electronic instrument provided with a circuit board onwhich is mounted this embodiment of the semiconductor device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is now described in terms of a number of preferredembodiments, with reference to the drawings.

It should be noted that in order to render the drawings more easilyunderstandable, they are shown partially enlarged. In the descriptionhereunder, because the final result envisaged is a single device, theremay be slight inconsistencies in the terminology and grammar used. Inthe description hereunder, the term “semiconductor element” is employed,and this refers, as the words suggest, to a chip-form object, but theterm “semiconductor elements” relating to the present invention is notrestricted to a semiconductor chip, but may also include reference to awafer form not yet separated into chips. In other words, here a“semiconductor element” may be in any form so long as it is a portion ofa base substrate formed of for example silicon on which a circuit isformed, and which can be used once in the separated state, or equally tothe same while in the integral state. In the description of wires andthe like, where necessary a representative portion only is discussed,and therefore other similar parts of the construction shown in thedrawings and other parts of the construction are omitted.

First Embodiment

FIG. 1 is a sectional view showing a first embodiment of thesemiconductor device. In this figure, a semiconductor device 10 is a CSPtype with a package size approximately equal to a semiconductor chip 12.on an active surface 12 a of the semiconductor chip 12, a plurality ofelectrodes 14 of for example aluminum (Al) are formed. On thesemiconductor chip 12 avoiding at least a part of each electrode 14, apassivation film 11 is formed. The passivation film is formed avoidingat least a part of each electrode because an electrical signal or thelike has to be led from the electrode 14. Therefore, the passivationfilm 11 has to avoid the electrode 14 so that an electrical signal orthe like can be led from the electrode. The passivation film can beformed of, for example, SiO₂, SiN, polyinide resin, or the like. On theactive surface 12 a, avoiding the electrode 14, an intermediate layer 16is formed. In more detail, the intermediate layer 16 is formed on thepassivation film not shown in the drawings. In the intermediate layer 16a depression 16 a is formed, and within the depression 16 a the activesurface 12 a is exposed. It is sufficient for the depression 16 a to beconcave, and the active surface 12 a is not necessarily exposed. Theintermediate layer 16 has a bevel 16 b sloping from the electrode 14,and a wire 18 is formed from the electrode 14 via the bevel 16 b ontothe intermediate layer 16. The opening outline of the depression 16 ashown in FIG. 1 is considerably larger than the size of the root portionof the external electrode 26, but this is not limiting on the invention,and it may be approximately equal in size to the root portion of theexternal electrode 26 or not smaller than the same. The opening of thedepression 16 a may be positioned under a part of the root portion ofthe external electrode 26. In this case, this opening allows thedeformation of the intermediate layer to achieve the stress absorptionfunction. The depression 16 a may be formed to penetrate theintermediate layer 16 and expose the underlying passivation film 11, butequally the bottom of the depression 16 a may not penetrate theintermediate layer 16 and leave a portion of the intermediate layer 16.

Here, the intermediate layer 16 is formed of an insulating resin, forexample polyimide resin, and when the semiconductor device 10 is mountedon a circuit board (not shown in the drawings), is able to absorb thestress generated by the difference in coefficient of thermal expansionbetween the semiconductor chip 12 and the circuit board on which it ismounted. It should be noted that the fact of the intermediate layer 16having a stress absorption function is not an essential element of thepresent invention. The stress absorption function may also be achievedby forming the depression 16 a (as described in detail below).

The insulating resin provides insulation to the wire 18, and can protectthe active surface 12 a of the semiconductor chip 12, providing heatresistance when the solder is fused during mounting. When the additionof the stress absorption function described below is considered, apolyimide resin or the like is generally used, and it is preferable touse one of these with a low Young's modulus (for example an olefinpolyimide resin, or the Dow Chemical Company's BCB or the like as anexample of other than a polyimide resin), and in particular, it ispreferable that the Young's modulus be not more than about 300 kg/mm².The thicker the intermediate layer 16 is, the greater the stressabsorbing ability, but when the size and cost of the semiconductordevice are considered, a thickness of between 1 and 100 μm ispreferable. However, when a polyimide resin with a young s modulus onthe order of 300 kg/mm² is used, a thickness of 10 μm or thereaboutswill suffice.

Alternatively, as the intermediate layer 16 may be used, for example, asilicone denatured polyimide resin, epoxy resin, silicone denaturedepoxy resin, or the like, and furthermore, a material with a low Young'smodulus capable of effecting stress absorption may be used. As theintermediate layer 16, a passivation layer (SiN, SiO₂, MgO, or the like)may be formed, and the stress absorption as such may be provided asdescribed below by the depression 16 a being formed.

The wire 18 is formed of for example copper (Cu), chromium (Cr),titanium (Ti), nickel (Ni), titanium-tungsten (Ti—W), or a laminatedplurality thereof, and thereon conductive foil 22 is formed. Theconductive foil 22 is previously formed on a substrate 20, and is thenadhered on the wire 18 together with the substrate 20, by means of anadhesive 24. It should be noted that the conductive foil 22 is alsoformed of for example copper (Cu).

The conductive foil 22 is formed to be larger than the opening outlineof the depression 16 a formed in the intermediate layer 16, and isdisposed so as to cover the depression 16 a. A part of the conductivefoil 22 contacts the wire 18 and is electrically connected thereto. Itshould be noted that it is preferable for the conductive foil 22 andwire 18 to be welded together by the application of heat and pressure.The electrical connection between the conductive foil 22 and wire 18,may be achieved as described above by the mechanical adhesion of theadhesive 24, or the wire 18 and conductive foil 22 may be brazedtogether by plating with gold (Au), tin (Sn), solder, or the like on thetwo, or again they may be joined by diffusion bonding using ultrasonicwelding or the like. For this reason, on at least one of the matingsurfaces of the conductive foil 22 and wire 18, it is preferable toprovide a low-temperature solder.

The substrate 20 is in the form of a film formed of a flexible resin orthe like, and has a penetrating hole 20 a formed over the depression 16a. It should be noted that the conductive foil 22 is formed so as tocover the penetrating hole 20 a on the underside of the substrate 20. Anexternal electrode 26 is formed on the conductive foil 22 so as toextend through the penetrating hole 20 a. The external electrode 26 maybe formed, for example, of solder only, or by plating the surface ofcopper (Cu) or nickel (Ni) with solder or gold.

It should be noted that the substrate 20 with attached conductive foil22 may also be a two-layer (copper foil+polyimide substrate) or athree-layer (copper foil+adhesive+polyimide substrate) film carrier tapeor Flexible Printed Circuit (FPC) used in TAB technology.

This embodiment is constructed as described above, and provides thefollowing effect. In the semiconductor device 10, the conductive foil 22on which the external electrode 26 is formed is supported by theintermediate layer 16. However, the intermediate layer 16 has thedepression 16 a formed in a region including immediately under theexternal electrode 26. By means of the depression 16 a, a space isformed under the conductive foil 22. In other words, close to thejunction with the external electrode 26, the conductive foil 22 is in afloating state, and is able to easily deform. Because of thisconstruction, when stress is applied to the external electrode 26, theconductive foil 22 and substrate 20 deform, and thereby the stress canbe absorbed. In this way, when the semiconductor device is mounted on acircuit board, or when the circuit board or electronic instrument inwhich it is mounted is subject to temperature variation, the resultingstress due to the difference in coefficient of thermal expansion betweenthe semiconductor device (or semiconductor chip formed of silicon) andthe circuit board, and the mechanical stress generated when bent byexternal stress, can be absorbed. Hereinbelow, the term “stress” refersto these.

Next, FIG. 2 shows a plan view of this embodiment of the semiconductordevice. In this figure, wires 18 are formed from the electrodes 14 ofthe semiconductor chip 12 toward the center of the active surface 12 a,and to each wire 18 is connected the conductive foil 22, and on theconductive foil 22 are provided external electrodes 26. Except for theregion of the external electrodes 26, the substrate 20 provides coveringand protection.

The electrodes 14 are positioned around the periphery of thesemiconductor chip 12, as an example of the so-called peripheralelectrode form, but equally an area array type of semiconductor chip inwhich electrodes are formed in an interior region within the peripheryof the semiconductor chip may be used.

It should be noted that as shown in this figure, the external electrodes26 are provided not over the electrodes 14 of the semiconductor chip 12,but in the region of the active surface of the semiconductor chip 12(the region in which the active element is formed). By providing theintermediate layer 16 in the active region, and further disposing(drawing-in) the wire 18 within the active region, the externalelectrodes 26 can be provided within the active region. In other words,a pitch conversion can be carried out. Therefore, the externalelectrodes 26 can be positioned within the active region, in otherwords, a region constituting a particular area, and the degree offreedom of positioning the external electrodes 26 is very greatlyincreased.

By bending the wire 18 at required positions, the external electrodes 26can be arranged on a grid. It should be noted that this is not anessential element of the present invention, and thus the externalelectrodes 26 may equally be provided so as not to be arranged on agrid.

In FIG. 2, at the junction of the electrode 14 and wire 18, the width ofthe electrode 14 and the width of the wire 18 are such that: wire18<electrode 14. But in practice, it is preferable that: electrode14≦wire 18. In particular, when electrode 14<wire 18, not only is theresistance or the wire 18 reduced, but since the strength is increasedwiring breaks are prevented.

It should be noted that in this embodiment, the intermediate layer 16has a stress absorption function, but by the mere fact that thedepression 16 a is formed, the stress can be absorbed. As a result, evenif the intermediate layer 16 is constructed as a layer of a materialwithout a stress absorption function (for example a simple insulatinglayer or protective layer), stress absorption is possible.

Next, FIGS. 3A to 3E illustrate the method of manufacturing thisembodiment of the semiconductor device. First, as shown in FIG. 3A, asemiconductor chip 12 having electrodes 14 of for example aluminum isreadied. It should be noted that on the semiconductor chip 12, avoidingthe electrode 14, a passivation film not shown in the drawings isformed. When the process of the present invention is applied to asemiconductor chip in wafer form, a commercially available wafer may beused. On the active surface 12 a of the semiconductor chip 12, apolyimide resin not shown in the drawings is provided by spin coating orthe like. Alternatively, a polyimide resin or the like in film form maybe previously adhered to the active surface 12 a.

Next, by a process of photolithography, as shown in FIG. 3B, theintermediate layer 16 having the depression 6 a is formed. It should benoted that when the depression 16 a is formed by photolithography, it ispreferable that a material appropriate therefor be seleeted for theintermediate layer 16.

Next, as shown in FIG. 3C, a wire 18 is formed extending from theelectrode 14 over the intermediate layer 16. For example, by sputteringa 100-angstrom (10⁻¹ m) layer of titanium-tungsten (Ti—W) is formed,then similarly by sputtering a 1 μm layer of copper (Cu) is formedthereon. The metal film thus obtained is then etched to a requiredpattern to form the wire 18.

Then as shown in FIG. 3D, with an adhesive 24 interposed, the substrate20 is adhered. In the substrate 20 a penetrating hole 20 a has beenpreviously formed, and in the position covering the penetrating hole 20a the conductive foil 22 is provided.

It should be noted that it is preferable that at least one of the matingsurfaces of the conductive foil 22 and wire 18, is plated with forexample, tin (Sn), gold (Au), or solder, and a low-temperature solderprovided.

Next the substrate 20 is placed in position so that the conductive foil22 contacts the wire 18, and heat and pressure is applied from above thesubstrate 20. In this way, the low-temperature solder fuses, and theconductive foil 22 and wire 18 are electrically connected. Thisconnection may also be carried out by the application of ultrasound orthe like.

Next, as shown in FIG. 3E, the external electrode 26 is formed on theconductive foil 22 so as to extend through the penetrating hole 20 a ofthe substrate 20. For example, solder balls may be placed on theconductive foil 22, solder plating may be applied, a solder paste may beprinted, or plating with copper (Cu) or nickel (Ni) or both may becarried out and further solder or gold (Au) plating carried out to formthe external electrode 26.

By means of the above process, the semiconductor device 10 can beobtained. It should be noted that in the case that the semiconductorchip 12 is in wafer form, dicing is then carried out to yield thesemiconductor device 10. The semiconductor device 10 is then subjectedto quality inspection and packed in trays.

It should be noted that in this embodiment, the wire 18 is formed on thebevel 16 b, but may equally be formed on the bevel on the side of thedepression 16 a. The same is also true of the following embodiments. Ifthis is done, the majority of the wire 18 passes over the intermediatelayer 16 and is protected, thus improving the device reliability.

Second Embodiment

FIG. 4 shows a second embodiment of the semiconductor device. In thisfigure, a semiconductor device 30 is characterized by having thedepression 16 a of the semiconductor device 10 shown in FIG. 1 filledwith a resin 32, but is otherwise of the same construction as thesemiconductor device 10. The opening outline of the depression 16 ashown in FIG. 4 is considerably larger than the size of the root portionof the external electrode 26, but this is not limiting on the invention,and it may be approximately equal in size to the root portion of theexternal electrode 26 or not smaller than the same. The opening of thedepression 16 a may be positioned under a part of the root portion ofthe external electrode 26. In this case, this opening allows thedeformation of the intermediate layer to achieve the stress absorptionfunction. The depression 16 a may be formed to penetrate theintermediate layer 16 and expose the underlying passivation film (notshown in the drawings), but equally the bottom of the depression 16 amay not penetrate the intermediate layer 16 and leave a portion of theintermediate layer 16.

As the resin 32, is preferably used a polyimide resin, a silicon gel orrubber or the like such as is used, for example, as a photosensitiveresist, selected to be soft, having a Young's modulus lower than theintermediate layer 16. If this is done, since the space formed by thedepression 16 a can be filled, when heat is applied in reflow processesand so forth, the occurrence of cracks due to the expansion of air orsteam can be prevented.

The resin 32 may be inserted before applying the substrate 20, or a holemay be formed in the substrate 20, and the resin inserted through thehole after applying the substrate 20.

The filling of the depression with resin as in this embodiment canequally be applied to all of the below embodiments.

Third Embodiment

FIG. 5 shows a third embodiment of the semiconductor device. In thisfigure, a semiconductor device 40, like the semiconductor device 10shown in FIG. 1, has a semiconductor chip 12, electrode 14, intermediatelayer 16, and wire 18, and in the intermediate layer 16 a depression 16a is formed.

On the intermediate layer 16 a substrate 42 is adhered by an adhesive24. The substrate 42 is a film formed of, for example, a material suchas the polyimide resin cited in the first embodiment for the material ofthe intermediate layer 16, having a low Young's modulus. On thesubstrate 42, a conductive foil 44 is formed patterned in the formed ofa wire, and on the conductive foil 44 an external electrode 46 isformed. In the substrate 42 over the portion of the wire 18 positionedover the intermediate layer 16, a penetrating hole 42 a is formed. Inthe penetrating hole 42 a, an electrical junction 48 is formed, so thatthe conductive foil 44 and wire 18 are electrically connected. On theconductive foil 44, a solder resist layer 49 is formed to avoid theexternal electrode 46, and protecting the conductive foil 44.

Next, the method of manufacturing the semiconductor device 40 isdescribed. First, in the steps shown in FIGS. 3A to 3C, on thesemiconductor chip 12 the intermediate layer 16 and wire 18 are formed,and the depression 16 a is formed in the intermediate layer 16.

Then on the intermediate layer 16, the substrate 42 is adhered by theadhesive 24, and the penetrating hole 42 a is formed in the substrate42. It should be noted that equally the penetrating hole 42 a may beformed in the substrate 42 first, and then the adhesion step carriedout.

Next, the conductive foil 44 is formed on the substrate 42. Theconductive foil 44 can be formed, for example, by sputtering,electroplating, electroless plating, or the like. For the patterning ofthe conductive foil 44, photolithographic technology may be used.Alternatively, a pre-patterned conductive foil 44 may be provided on thesubstrate 42, and this then adhered on the intermediate layer 16.

Then, for example by electroless plating, or by the supplementing ofelectroplating, or other methods, the electrical junction 48 isprovided, in a region including the penetrating hole 42 a in thesubstrate 42.

Next, on the conductive foil 44, the solder resist layer 49 is provided,avoiding the region of formation of the external electrode 46, and thenthe external electrode 46 is formed. The method of formation of theexternal electrode 46 is the same as the method of formation of theexternal electrode 26 in the first embodiment.

With the semiconductor device 40 fabricated as described above, againthe depression 16 a is formed in the intermediate layer 16, andtherefore stress applied to the external electrode 26 can be absorbed.

Fourth Embodiment

FIG. 6 shows a fourth embodiment of the semiconductor device. In thisfigure, a semiconductor device 50, like the semiconductor device 10shown in FIG. 1, has an intermediate layer 56 formed on a semiconductorchip 52 which has an electrode 54, and in the intermediate layer 56 adepression 56 a is formed. A wire 58 is formed from the electrode 54over the intermediate layer 56, and a conductive foil 60 is formed onthe intermediate layer 56 integrally with the wire 58. In the conductivefoil 60, at least one hole 60 a is formed. Then over the region of thedepression 56 a in the conductive foil 60, an external electrode 62 isformed. A solder resist layer 64 is formed on and protects the wire 58and conductive foil 60, avoiding the external electrode 62.

This embodiment has a characteristic method of manufacture. FIGS. 7A toBC illustrate the method of manufacturing this embodiment of thesemiconductor device.

In this embodiment, since a substrate is not used, it is preferable thatafter the intermediate layer 56, external electrode 62, and the like areformed on a wafer, this is subjected to dicing. In contrast to this, inembodiments where a substrate is used (the first to third embodiments),it is possible to adhere individual semiconductor chips on a substratein tape form.

First, as shown in FIG. 7A, on an active surface 52 a of thesemiconductor chip 52, the intermediate layer 56 is formed, avoiding theelectrode 54. The intermediate layer 56 is formed of a material similarto that of the intermediate layer 16 shown in FIG. 1. When theintermediate layer 56 is formed of a material with a low Young'smodulus, the stress absorption function is achieved by the intermediatelayer 56. Alternatively, the intermediate layer 56 may be formed of ahard material which does not provide a stress absorption function (forexample, an inorganic substance such as magnesium oxide (MgO) or thelike).

It should be noted that when the intermediate layer 56 is etched in alater step, in order that the active surface 52 a of the semiconductorchip 52 is not etched, it is preferable that the intermediate layer 56have a different material composition from the semiconductor passivationfilm. For this reason it is preferable that the intermediate layer 56 isformed of a substance which can be etched under conditions such that thematerial of the exposed surface of the semiconductor chip 52 is notetched.

Next, as shown in FIG. 7B, a metal film 66 is formed from the electrode54 over the intermediate layer 56. The method of manufacture thereof isthe same as the method of forming a metal film by which the wire 18 ofthe first embodiment is formed. In this case, since the stress of anexternal electrode 62 described below is directly applied to the wire58, it is preferable for the thickness of the wire 58 to be between 5and 20 μm or thereabouts. The metal film 66 is etched in a stepdescribed below, and thus the wire 58 and conductive foil 60 are formed.

Next, as shown in FIG. 7C, holes 60 a are formed in the metal film 66 inthe portion which will form the conductive foil 60, and through theholes 60 a, the intermediate layer 56 is exposed to an etching fluid oretching gas (etchant). For example, when the intermediate layer 56 isformed of a polyimide or similar resin, as the etchant is preferablyused KOH or a similar strong alkali in aqueous solution, or a dryetching gas such as O₂ or CF₄, and when the intermediate layer 56 isformed of magnesium oxide (MgO) or the like, a hot phosphate aqueoussolution or the like is preferable. Thereafter, the etchant is removedas required. In particular, in the case of a wet process, washing andrinsing steps are preferably added. In this way, as shown in FIG. 7D,the intermediate layer 56 is etched to form the depression 56 a.

Next, as shown in FIG. 8A, the metal film 66 is patterned, and the wire58 and conductive foil 60 are formed. Then as shown in FIG. 8B, thesolder resist layer 64 is formed, and as shown in FIG. 8C the externalelectrode 62 is formed. As a solder resist is commonly used aphotosensitive polyimide resin or epoxy resin dry film or the like. Themethod of forming the external electrode 62 is the same as in the firstembodiment. In this way, the semiconductor device 50 is obtained. Inthis embodiment again, an effect similar to that of the first embodimentcan be obtained.

Furthermore, the semiconductor device 50 fabricated according to thisembodiment has holes 60 a formed in the conductive foil 60, and theconductive foil 60 is thus more easily deformed. As a result, the stressabsorption effect of the conductive foil 60 which is thus floating overthe depression 56 a is further improved.

Fifth Embodiment

FIGS. 9A to 9C show the method of manufacturing a fifth embodiment ofthe semiconductor device.

In this embodiment, as shown in FIG. 9A, an intermediate layer 76 isformed on a semiconductor chip 72 having an electrode 74. On theintermediate layer 76 a conductive foil 80 is formed, and a wire 78 isformed from the conductive foil 80 to reach the electrode 74. On thewire 78 and conductive foil 80, a solder resist layer 84 is formed. Inthe conductive foil 80 a hole 80 a is Formed.

It should be noted that the method of formation of the intermediatelayer 76 is the same as the method shown in FIG. 7A, and the method offormation of the wire 78, hole 80 a, and conductive foil 80 is the sameas shown in FIGS. 7B to 8A. A solder resist layer 84 is formed in aregion to avoid the external electrodes 82 (see FIG. 9B).

Then the external electrode 82 is formed on the conductive foil 80, andthe concomitant residue is removed, and on the external electrode 82 andsolder resist layer 84, a covering layer 86 is formed (see FIG. 9B). Thecovering layer 86 is formed of a material which is not easily etchedunder the etching conditions of the intermediate layer 76.

Next, through the hole 80 a in the conductive foil 80, by the same stepas is shown in FIG. 7D, a depression 76 a is formed in the intermediatelayer 76, the covering layer 86 is removed, and the semiconductor device70 shown in FIG. 9C is obtained.

According to this embodiment, the residue created when the externalelectrode 82 is formed is removed before the depression 76 a is formedin the intermediate layer 76, and therefore there is no residueremaining in the depression 76 a. The features of a semiconductor device70 fabricated according to this embodiment are the same as in the fourthembodiment.

Sixth Embodiment

FIGS. 10A to 10C show the method of manufacturing a sixth embodiment ofthe semiconductor device.

In this embodiment, as shown in FIG. 10A, a semiconductor chip 102 isused in which a passivation film 106 is formed on an active surface 102a avoiding an electrode 104. The passivation film 106 is formed of amaterial sharing the properties of an intermediate layer 108 shown inFIG. 10C. In other words, the passivation film 106 is formed of amaterial which is etched under the etching conditions of theintermediate layer 108. For example, the intermediate layer 108 andpassivation film 106 may both be formed of a polyimide resin.

In a case such as this, as shown in FIG. 10B, a covering layer 118 isformed on the passivation film 106, at least in the position under thedepression 108 a (see FIG. 10C). The covering layer 118 is formed of amaterial which is not etched under the etching conditions of theintermediate layer 108 and passivation film 106. For example, when theintermediate layer 108 and passivation film 106 are formed of polyimideresin, the covering layer 118 may be formed of a thin metal film of Cr,Ti—W, Ti, or the like.

Thereafter, by the same process as is shown in FIGS. 7A to 8C, as shownin FIG. 10C the intermediate layer 108 having a depression 108 a, a wire110, a conductive foil 112 having a hole 112 a, an external electrode114 and a solder resist layer 116 are formed.

According to this embodiment, since the passivation film 106 is coveredby the covering layer 118, when the intermediate layer 108 is etched toform the depression 108 a, etching as far as the passivation film 106can be prevented. In this way, exposure of the active element within thedepression 108 a can be prevented. The characteristics of the stressabsorption function are the same as in the above described embodiments.

Seventh Embodiment

FIGS. 11A and 11B show a part of a seventh embodiment of thesemiconductor device. It should be noted that FIG. 11B is a sectionalong the line B—B in FIG. 11A. In this embodiment, a semiconductordevice 120 has holes 122 and 124 formed in the substrate 20 andconductive foil 22 of the semiconductor device 10 shown in FIG. 1.

According to this embodiment, by the formation of the holes 122 and 124,the substrate 20 and conductive foil 22 are rendered more easilydeformable, and the stress absorption function is increased.

Eighth Embodiment

FIG. 12 shows an eighth embodiment of the semiconductor device. In thisfigure, a semiconductor device 130 has a wire 136 formed on the activesurface 132 a of a semiconductor chip 132 from an electrode 134. Overthe wire 136 an intermediate layer 138 is formed. Then in theintermediate layer 138 a depression 138 a is formed, positioned over thewire 136, so as to expose the wire 136. On the intermediate layer 138 asubstrate 146 is applied by an adhesive 142. On the substrate 146, in aposition above the depression 138 a and on the surface facing thedepression 138 a a conductive foil 144 is formed. In the substrate 146above the depression 138 a a penetrating hole 146 a is formed, so thatthe conductive foil 144 is exposed on the opposite surface. Then anexternal electrode 148 is formed through the penetrating hole 146 a.

Furthermore, the depression 138 a is filled with a conductive paste 140.The conductive paste 140 is a soft resin similar to the resin 32 withwhich the depression 16 a shown in FIG. 4 is filled, with the additionof a conducting filler such as silver (Ag), copper (Cu), silver-platedcopper, gold (Au), or the like. By means of this conductive paste 14,the wire 136 and conductive foil 144 are electrically connected.

In this embodiment again, by virtue of the fact that the depression 138a is formed in the intermediate layer 138, the stress absorptionfunction can be achieved.

Ninth Embodiment

FIGS. 13A to 14B show the method of manufacturing a ninth embodiment ofthe semiconductor device. In this embodiment, a semiconductor chip 152is used which, like the semiconductor chip 102 shown in FIG. 10A, has apassivation film (not shown in the drawings) formed on an active surface152 a. This passivation film is formed of a material which is etchedunder the etching conditions or an intermediate layer 158.

As shown in FIG. 13A, a covering layer 156 is formed over thepassivation film on the active surface 152 a. The covering layer 156 isformed of a material (for example, chromium (cr), titanium (Ti),titanium-tungsten (Ti—W), copper (Cu), or the like) which is not etchedunder the etching conditions of the intermediate layer 158. The coveringlayer 156 is formed, for example, by sputtering.

Next, as shown in FIG. 13B, the intermediate layer 158 is formedavoiding an electrode 154 including the covering layer 156. The materialof the intermediate layer 158 is the same as in the first embodiment.

Then as shown in FIG. 13C, a wire 160 is formed from the electrode 154over the intermediate layer 158, and a conductive foil 162 is formed toprovide electrical connection to the wire 160. More specifically, bysputtering, a metal film of chromium (Cr), titanium (Ti),titanium-tungsten (Ti—W), copper (Cu), or a laminated plurality thereof,is formed, and this is patterned by etching, to form integrally the wire160 and conductive foil 162. A hole 162 a is formed in the conductivefoil 162.

Next, as shown in FIG. 13D, an external electrode 164 is formed on theconductive foil 162. More specifically, on the conductive foil 162,bumps of copper (Cu), nickel (Ni), gold (Au), or a laminated pluralitythereof are formed by electroplating or electroless plating, to form theexternal electrode 164.

Then as shown in FIG. 14A, a solder resist layer 166 is formed on thewire 160, and on the solder resist layer 166 a covering layer 168 isformed. The covering layer 168 is also formed of a material (forexample, chromium (Cr), titanium (Ti), titanium-tungsten (Ti—W), copper(Cu), or the like) which is not etched under the etching conditions ofthe intermediate layer 158.

Then as shown in FIG. 14B, a depression 158 a is formed in theintermediate layer 158. This step is similar to the step shown in FIG.7D. The covering layer 168 is removed by etching. In this example, theexternal electrode 164 has an opening in the center, but the openingdesign may equally be as in the seventh embodiment.

By means of the above process, a semiconductor device 150 can beobtained. The semiconductor device 150 also achieves a stress absorptionfunction by virtue of the depression 158 a being formed in theintermediate layer 158.

It should be noted that in place of the bump-form external electrode 164of the semiconductor device 150 shown in FIG. 14D, as shown in FIG. 15,an external electrode 170 may be formed from a solder ball on the edgeof the hole 162 a formed in the conductive foil 162.

It should be noted that present invention is not restricted to a CSPtype semiconductor device. For example, if a deforming portion islaminated directly on the electrodes of the semiconductor chip, asemiconductor device with a stress absorption function, while of asimilar size to flip-chip, is obtained.

In FIG. 16 is shown a circuit board 1000 on which is mounted asemiconductor device 1100 fabricated by the method of the abovedescribed embodiment. The circuit board 1000 generally uses an organicsubstrate such as for example a glass epoxy substrate. On the circuitboard 1000, a wire pattern of for example copper is formed as a desiredcircuit, and on the circuit board 1000 are provided solder balls. Thenby mechanically connecting the solder balls of the wire pattern and theexternal electrodes of the semiconductor device 1100, an electricalconnection between the two is achieved.

In this case, since the construction is such that strain caused in thesemiconductor device 1100 by differences in thermal expansion with thesurroundings can be absorbed, even when this semiconductor device 1100is mounted on the circuit board 1000, both at the time of connection andthereafter, the reliability can be improved.

It should be noted that the mounting area can be reduced to the mountingarea for bare chip mounting. For this reason, when this circuit board1000 is used in an electronic instrument, the electronic instrumentitself can be made more compact. Within the same area, a larger mountingarea is available, and higher functionality can also be achieved.

As an example of an electronic instrument provided with this circuitboard 1000, FIG. 17 shows a notebook personal computer 1200.

It should be noted that, the present invention can be applied to anysurface-mounted electronic component, whether active or passive.Electronic components include, for example, resistors, capacitors,coils, oscillators, filters, temperature sensors, thermistors,varistors, variable resistors, and fuses.

What is claimed is:
 1. A semiconductor device comprising: asemiconductor element that includes a plurality of electrodes; apassivation film formed on a surface of said semiconductor element in aregion avoiding at least a part of each of said electrodes; a conductivefoil formed at a given spacing from the surface on which saidpassivation film is formed; external electrodes formed on saidconductive foil; an intermediate layer formed between said passivationfilm and said conductive foil to support said conductive foil; and wireselectrically connecting said electrodes to said conductive foil; whereina depression opening between said conductive foil to said passivationfilm is formed in said intermediate layer under a part of saidconductive foil that includes the connection with said externalelectrodes.
 2. The semiconductor device as defined in claim 1, whereinsaid depression is filled with a resin having a Young's modulus lowerthan that of said intermediate layer.
 3. The semiconductor device asdefined in claim 2, wherein said wires are formed on the surface onwhich said passivation film is formed, and are positioned on the bottomsurface of said intermediate layer depression; and wherein said resinhas a conducting filler added, and electrically connects said wires tosaid conductive foil.
 4. The semiconductor device as defined in claim 3,wherein said conductive foil has a hole positioned within an openingedge of said depression and avoiding the connection with said externalelectrodes.
 5. The semiconductor device as defined in claim 3, furthercomprising a substrate with a surface on which said conductive foil isformed, said surface facing toward said intermediate layer, wherein saidsubstrate has a penetrating hole over said depression; and wherein saidexternal electrodes are formed on said conductive foil through saidpenetrating hole.
 6. The semiconductor device as defined in claim 3,wherein a substrate formed of a flexible material is provided betweensaid intermediate layer and said conductive foil; wherein said substratehas a penetrating hole in a region avoiding above said depression; andwherein said wires and said conductive foil are electrically connectedthrough said penetrating hole.
 7. The semiconductor device as defined inclaim 1, wherein said intermediate layer has a bevel between saidelectrode and said conductive foil; and wherein said wires are formed onsaid bevel to electrically connect said electrode to said conductivefoil.
 8. The semiconductor device as defined in claim 7, wherein saidconductive foil has a hole positioned within an opening edge of saiddepression and avoiding the connection with said external electrodes. 9.The semiconductor device as defined in claim 7, further comprising asubstrate with a surface on which said conductive foil is formed, saidsurface facing toward said intermediate layer, wherein said substratehas a penetrating hole over said depression; and wherein said externalelectrodes are formed on said conductive foil through said penetratinghole.
 10. The semiconductor device as defined in claim 7, wherein asubstrate formed of a flexible material is provided between saidintermediate layer and said conductive foil; wherein said substrate hasa penetrating hole in a region avoiding above said depression; andwherein said wires and said conductive foil are electrically connectedthrough said penetrating hole.
 11. The semiconductor device as definedin claim 1, wherein said intermediate layer is formed of a flexiblematerial.
 12. The semiconductor device as defined in claim 1, whereinsaid conductive foil has a hole positioned within an opening edge ofsaid depression and avoiding the connection with said externalelectrodes.
 13. The semiconductor device as defined in claim 1, furthercomprising a substrate with a surface on which said conductive foil isformed, said surface facing toward said intermediate layer, wherein saidsubstrate has a penetrating hole over said depression; and wherein saidexternal electrodes are formed on said conductive foil through saidpenetrating hole.
 14. The semiconductor device as defined in claim 1,wherein a substrate formed of a flexible material is provided betweensaid intermediate layer and said conductive foil; wherein said substratehas a penetrating hole in a region avoiding above said depression; andwherein said wires and said conductive foil are electrically connectedthrough said penetrating hole.
 15. The semiconductor device as definedin claim 1, wherein said conductive foil and said wires are formedintegrally.
 16. The semiconductor device as defined in claim 1, whereinsaid conductive foil and said wires are formed separately.
 17. A circuitboard on which is mounted the semiconductor device as defined in claim1.
 18. An electronic instrument having the circuit board as defined inclaim
 17. 19. The semiconductor device as defined in claim 1, whereinsaid depression in said intermediate layer is concave.
 20. A method ofmanufacturing a semiconductor device, comprising the steps of: providinga semiconductor element that includes a plurality of electrodes and apassivation film that is formed on a surface of said semiconductorelement in a region avoiding at least a part of each of said electrodes;forming a conductive foil at a given spacing from the surface on whichsaid passivation film is formed; forming external electrodes on saidconductive foil; forming an intermediate layer between said passivationfilm and said conductive foil to support said conductive foil; forming adepression opening between said conductive foil to said passivation filmin said intermediate layer under a part of said conductive foil thatincludes the connection with said external electrodes and in a positionto avoid said electrodes; and forming wires that connect electricallysaid electrode to said conductive foil; said external electrodes areformed on said conductive foil in a position above said depression. 21.The method of manufacturing a semiconductor device as defined in claim20, wherein: a substrate is provided, having a penetrating hole, andhaving said conductive foil adhered to a position including the positionover said penetrating hole; said intermediate layer is formed on thesurface on which said passivation film is formed, and said depression isformed in said intermediate layer; thereafter, said substrate is mountedon said intermediate layer so that said penetrating hole is positionedover said depression and that said conductive foil is opposed to saiddepression; and said external electrodes are formed on said conductivefoil through said penetrating hole.
 22. The method of manufacturing asemiconductor device as defined in claim 20, wherein: a substrate formedof a flexible material and having a penetrating hole is provided; saidintermediate layer is formed on the surface on which said passivationfilm is formed, said depression is formed on said intermediate layer,and said wires are formed on said intermediate layer; and said substrateis mounted on said intermediate layer with said penetrating holepositioned over said wires, said conductive foil is formed on saidsubstrate, and said wires and said conductive foil are electricallyconnected through said penetrating hole.
 23. The method of manufacturinga semiconductor device as defined in claim 20, wherein said intermediatelayer is formed on the surface on which said passivation film is formed,said conductive foil is formed on said intermediate layer, a hole isformed in said conductive foil, and said intermediate layer is etchedthrough said hole to form said depression.
 24. The method ofmanufacturing a semiconductor device as defined in claim 23, whereinsaid intermediate layer is formed of a material which can be etchedunder conditions in which said semiconductor element cannot be etched.25. The method of manufacturing a semiconductor device as defined inclaim 24, further comprising: before the step of etching saidintermediate layer, a step in which said external electrodes are formedon said conductive foil, and on said external electrodes an electrodecovering layer is formed of a material which is not readily etched underthe etching conditions of said intermediate layer.
 26. The method ofmanufacturing a semiconductor device as defined in claim 23, furthercomprising: before the step of etching said intermediate layer, a stepin which said external electrodes are formed on said conductive foil,and on said external electrodes an electrode covering layer is formed ofa material which is not readily etched under the etching conditions ofsaid intermediate layer.
 27. The method of manufacturing a semiconductordevice as defined in claim 20, wherein: said passivation film is etchedunder the etching conditions of said intermediate layer; and on saidpassivation film, a covering layer is formed of a material which is notreadily etched under the etching conditions of said intermediate layer,said intermediate layer is formed on said covering layer, saidconductive foil is formed on said intermediate layer, a hole is formedin said conductive foil, and said intermediate layer is etched throughsaid hole to form said depression.
 28. The method of manufacturing asemiconductor device as defined in claim 27, further comprising: beforethe step of etching said intermediate layer, a step in which saidexternal electrodes are formed on said conductive foil, and on saidexternal electrodes an electrode covering layer is formed of a materialwhich is not readily etched under the etching conditions of saidintermediate layer.
 29. The method of manufacturing a semiconductordevice as defined in claim 20, wherein; said passivation film is etchedunder the etching conditions of said intermediate layer; on saidpassivation film, a first covering layer is formed of a material whichis not readily etched under the etching conditions of said intermediatelayer; said intermediate layer is formed on said first covering layer;said conductive foil and wires are formed on said intermediate layer,and a hole is formed in said conductive foil; a solder resist layer isformed on said wires; on said solder resist layer, a second coveringlayer is formed of a material which is not readily etched under theetching conditions of said intermediate layer; and said intermediatelayer is etched as far as the underneath of said conductive foil throughsaid hole in said-conductive foil.
 30. The method or manufacturing asemiconductor device as defined in claim 29, further comprising: beforethe step of etching said intermediate layer, a step in which saidexternal electrodes are formed on said conductive foil, and on saidexternal electrodes an electrode covering layer is formed of a materialwhich is not readily etched under the etching conditions of saidintermediate layer.
 31. The method of manufacturing a semiconductordevice as defined in claim 20, further comprising a step in which saiddepression is filled with a resin having a Young's modulus lower thanthat of said intermediate layer.
 32. The method of manufacturing asemiconductor device as defined in claim 20, wherein said depression insaid intermediate layer is concave.